It is well known that any telephone exchange requires a preliminary verification of the incoming signals in order to eliminate spurious signals and to send only properly encoded signals to the control units designed to identify the signaling criteria.
In conventional electromechanical exchanges, such verification is carried out by groups of circuits, referred to as translators, which are associated with each trunk. In the large modern exchanges, where the ever-increasing requirements for new services call for the use of either more and more complex signaling codes or more and more sophisticated connection and supervision procedures, the individual assignment of a translator to each trunk would require an excessive number of translators, giving rise to space and cost problems during installation and operation.
A first step in the solution of the problem was made in the register exchanges, through the utilization of ancillary centralized logical circuitry carrying out some of the logic functions of the translators.
Recently, the decision and control units have been increasingly centralized and the higher speed of the electronic systems has been exploited through the use of time-division techniques; consequently the centralized electronic units were also assigned functions which had been handled by peripheral equipment in the earlier exchanges, thus leaving only some essential functions decentralized.
In the most modern highly centralized electronic exchanges, the traditional translators are replaced by simple circuits scanning the trunks and sampling the signals appearing thereon.